Accurate vehicle velocity estimation is crucial for reliable performance of the vehicle's traction and stability control systems. Longitudinal velocity and lateral velocity are vehicle dynamic variables used by vehicle control systems. Longitudinal speed is a vehicle dynamic variable used for example by adaptive cruise control systems and antilock braking systems. Lateral velocity is a vehicle dynamic variable used for stability control systems. Longitudinal and lateral velocity are generally estimated via wheel speed sensors, and/or lateral acceleration sensors, and/or other inertia-based sensors. Often such sensors must be calibrated for sensor bias or the use of sensors having high accuracy must be utilized.
Many available longitudinal velocity estimation methods rely on vehicle planar kinematics to develop observers that use standard measurements from an inertial measurement unit (IMU) such as acceleration, yaw, pitch and roll rates without implementing a tire model. These methods may result in estimation errors, large oscillations and drift for high-slip conditions, and low performance for the combined-slip maneuvers because of not using a bounded and stable tire force model. Other methods utilize a tire model in the velocity estimation which also may be inaccurate as a result of unknown road friction and dependency to the tire parameters.
Tire forces can be measured at each corner, but their cost impact, calibration and maintenance are their major drawbacks to be used for production vehicles. Provided that the longitudinal tire force calculation needs road friction, even accurate slip ratio information from the GPS will not provide forces at each corner. Hence, it would be desirable to establish a reliable and computationally efficient algorithm, which is robust to road conditions and uncertainties and independent from wheel torques in order to improve the performance of the chassis control and active safety systems. An ideal system would provide a reliable longitudinal speed estimation at each corner and at the center of gravity independent from wheel torques and robust to the road condition for the vehicle's active safety control systems.